Like Bob Turner said, I have had sporadic problems with the 5 volt supply line. In my case it is NOT the GRT unit but rather my harness. In the first case, I found the crimp where I split the line to the two tanks was (to my great surprise) not good in my original manufacture. Replaced. Many flight hrs later with a reapearance of the problem, I found the industrial D-sub female pin that I used had loosened up on the male pin exiting the EIS. A light squeeze fixed it.
Many hrs passed and the issue recently returned so I will either squeeze it again or replace that female with the machined tubular aircraft female type. I bought some a while back, just for this eventuality.
RV-7A: Flying since April 15, 2012. 690hrs
YIO-360-M1B, mags, CS, GRT EX and WS H1s & A/P, Navworx
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